Changes of the hindwing motor pattern associated with phonotactic steering during flight in the cricket,Teleogryllus oceanicus

Abstract

1. The hindwing movements and flight motor pattern underlying straight flight and negative phonotactic steering of the cricketTeleogryllus oceanicus were investigated by photographing the wing movements and by recording electromyograms (EMG) from hindwing muscles. 2. During straight flight the right and left hindwings showed symmetrical strokes. When the animal turned in response to ultrasonic auditory stimuli the wing stroke was clearly asymmetrical. For animals tethered in an inverted position the hindwing outside the turn showed a lower elevation than the hindwing inside the turn. 3. The straight flight motor pattern showed the elevators were active at 45 to 57% of the depressor cycle. The latency from depressor to elevator activity (D-E) showed a positive correlation with the depressor period whereas the latency from elevator to depressor activity (E-D) was relatively independent of the depressor period. 4. The wing beat frequency increased when the animal steered in response to auditory stimuli. 5. During steering of an animal tethered in an inverted position the elevator muscles on the inside of a turn showed increased activity (double spikes). Also, on the inside of a turn the latency from depressor to elevator activity decreased and the phase of elevator activity in the depressor cycle decreased. On the outside of a turn the elevator muscles were less active. The latency from depressor to elevator activity increased as did the phase of elevator activity in the depressor cycle. 6. The increased activity and earlier firing of the elevators on the inside of a turn is consistent with a greater wing elevation on the same side. Similarly, the decreased activity and later firing of the elevator on the outside of a turn is consistent with a lower wing elevation on that side. These asymmetrical wing strokes seen in the hindwing could be important elements of steering.